Ion Fluxes Across the Transfusion Zone of Secreting Limonium Salt Glands Determined from Secretion Rates, Transfusion Zone Areas and Plasmodesmatal Frequencies

Faraday, C. D., Quinton, P. M. and Thomson, W. W. 1986. Ionfluxes across the transfusion zone of secreting Limonium saltglands determined from secretion rates, transfusion zone areasand plasmodesmatal frequencies.—J. exp. Bot. 37: 482–494. The epidermal salt-secreting glands of Limonium (Plumbaginaceae)are enclosed in a cuticular envelope. Ions and metabolites enterthe glands from the mesophyll through gaps in the cuticularenvelope, the transfusion zones. Net influxes of ions acrossthe transfusion zone were calculated from measurements of secretionrates and transfusion zone areas. When leaves of L. pereziiF. T. Hubb. were treated with 300 mol m^–3 NaCl, transfusionzone influxes of Na⁺ K⁺, Ca⁺⁺ and Cl^– as high as 7?0?10^–5,1.7?10^–5, 5?8?10^–7 and 8.5?10^–5 mol m^–2s^–1 respectively, were calculated. Assuming a transmembranepathway, these fluxes would be some of the highest reportedfor ions in plant cells. Key words: Salt glands, ion fluxes, ultrastructure     

Plant species richness in the mallee region of Western Australia

Sixteen sites (area 1000 m²) within the mallee region of southern Western Australia were sampled for vascular plant species richness. Species richness ranged from 17 species per 1000m² in a Halosarcia syncarpa salt-complex site and a Eucalyptus occidentalis tree mallee site, up to 48 species per 1000 m² in a Eucalyptus angulosa-Eucalyptus tetragona shrub mallee site. Woodland, woodland/mallee and mallee sites consisted mainly of perennial species while shrubland sites and salt-complex sites had a higher percentage of ephemeral species. Sites with the highest species richness occurred on soils with the lowest nutrient content. Sites with lowest species numbers were those with severe habitat conditions or where better nutrient conditions may have provided the dominants with a competitive advantage to suppress associated species.     

Evidence for the Bidirectional Replication of the <Emphasis Type="Italic">Escherichia coli</Emphasis> Chromosome

Experiments with transducing phage indicate that the circular chromosome of Escherichia coli is replicated in both directions from a fixed origin.     

Absence of a 5S RNA Component in the Mitochondrial Ribosomes of <Emphasis Type="Italic">Neurospora crassa</Emphasis>

RIBOSOME-BOUND, low molecular weight RNA, distinct from tRNA, was first observed in E. coli by Rosset and Monier¹. This RNA, which has a sedimentation coefficient of about 5S, is now considered to be a universal component of ribosomes. We report here our attempts to find low molecular weight RNAs other than tRNA in mitochondria of Neurospora. Our evidence suggests that the mitochondrial ribosomes of this organism lack a 5S RNA component.     

Cooling as Reinforcing Stimulus in Aplysia

An experiment was carried out to investigate the role of temperaturein the previously reported reinforcing effect of an increasein sea water level in Aplysia. In the present experiment, itwas found that the reinforcing effect of water level changeon rod-pressing behavior in Aplysia depends on a decrease intemperature associated with water level change. In order studymodification of rod pressing behavior produced by contingentincrease in water level and decrease in temperature, the rateand latency of rod-press responses in experimental animals wherecompared with those of yoked control animals exposed to non-contingentwater level and temperature change. Higher response rates andshorter response latencies were obtained from experimental overyoked control animals but only the shorter latencies of experimentalanimals were attributed to a behavioral change resulting fromcontingent water level and temperature reinforcement.     

New Reaction of <Emphasis Type="Italic">O</Emphasis>-Benzoquinone at the Thioether Group of Methionine

THERE are two biochemical systems which probably evolved before the development of accurate polynucleotide-specified protein synthesis: these are the system for polynucleotide replication and the machinery of protein synthesis itself^{1, 2}. Before accurately specified proteins became available, these processes were perhaps catalysed by polynucleotide enzymes. Both tRNA and rRNA, which can be viewed as polynucleotide enzymes, have persisted as indispensable components of the contemporary apparatus. This has led me to wonder whether polynucleotide enzymes might still be operative in DNA replication. Moreover, in view of the complexity which would have been required for even a rudimentary form of protein synthesis, it seems unlikely that tRNA and rRNA arose by chance in a single evolutionary step¹. More probably they have evolved from the replicative machinery for polynucleotides and thus it seems likely that the machinery of DNA replication may have many features in common with the polynucleotide components of protein synthesis.     

Efficacy of Monensin or Amprolium in the Prevention of Hepatic Coccidiosis in Rabbits

SYNOPSIS. New Zealand White rabbits were fed monensin (Coban® Premix) or amprolium in pelleted feed as a prophylaxis against infection with Eimeria stiedai. Rabbits receiving monensin at 0.005, 0.01, or 0.02% concentrations in the feed did not become infected but ate only small amounts of pellets when the drug concentration was 0.02%. All rabbits given 0.02% amprolium in pelleted feed developed severe infections. Rabbits on "limited" (8 gm pellets per day) diets were susceptible to infection.